The present invention relates to a film coating apparatus for coating a resist film on a substrate such as an LCD substrate and a semiconductor substrate.
In liquid crystal display (LCD) manufacturing processes, a photolithography technique is employed. In the photolithographic technique, a resist is first coated on a glass substrate and a predetermined pattern is then formed on the coated resist by exposing the resist to light followed by developing it. In this manner, a resist film having the predetermined pattern is formed on the surface of the glass substrate. If the resist pattern is further subjected to a film formation process and an etching process, a circuit formed of a semiconductor layer, an insulating layer and an electrode layer can be formed on the substrate in a predetermined pattern.
For example, U.S. Ser. No. 08/914,819 (filed on Aug. 20, 1997) discloses a resist coating apparatus for an LCD substrate having a slit nozzle. The conventional apparatus, as shown in FIG. 1, has a nozzle 1 having a linear slit-form discharge port 2. A passage 1a communicates with a resist solution supply source (not shown) and a liquid storage portion 1c of the nozzle 1 through an entrance 1b. The liquid storage portion 1c communicates with a slit-form discharge port 2. While a resist solution 3 is being discharged from the slit nozzle 1 in the form of a band, the nozzle 1 is moved along an LCD substrate from one side to the opposite side in a scanning manner, thereby coating the resist on the substrate.
In the nozzle 1 of the conventional apparatus, however, pressure P2 applied to the peripheral regions of the slit-form discharge port 2 tends to be higher than pressure p1 applied to the middle region thereof, with the result that the amount of the resist solution discharged from the peripheral regions is increased compared to that from the middle region. Consequently, the resist solution discharged from the peripheral regions becomes thicker than that from the middle region, as shown in FIG. 2. Furthermore, since the viscosity of the resist solution is influenced by the variance in discharge pressure of the resist solution, the resist solution discharged from both peripheral regions of the discharge port 2 becomes thick. Consequently, the resist film 4 formed an LCD substrate G is thick at the both lateral sides as shown in FIG. 3. As a whole, the resist film is formed with a non-uniform thickness, with the result that the product yield decreases.
In addition, when the film is formed by coating the resist solution discharged from the nozzle 1 on the LCD substrate, other factors such as ambient temperature and static electricity have effects on the resist film formation. Also for this reason, the resultant resist film becomes non-uniform.